Elucidation of Ion Exchange Property of Brown Coals in Relation to Their Higher Order Structure

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The present project aims at elucidating the ion exchange property of Australian brown coals, Yallourn and Loy Yang. The property is expected to be heavily dependent of the higher order structure of the coals. The main results obtained are as follows.1. Exchange of transition metal cations is found to proceed only slowly. By pre-exchanging the functional groups of coal with sodium or calcium, the exchange with iron or nickel cations were found to take place rapidly.2. The ability of coals to accept cations is largely suppressed by heat treatment, though the number of the acidic functional groups did not decrease so much. By adding to the exchange solution organic solvents such as acetone, methanol or ethanol, the extents of cation exchange of heat-treated coals were found to be promoted profoundly and the effects seem to correlate with the swelling of the coal.3. The rate of cation exchange is found to vary depending on the cation species and the temperature. The addition of ethanol did not change the rate, but the extent of cation exchange.4. The amount of extracted humic acid by alkali decreased with the temperature of heat treatment, but the exchange with calcium maintained the easiness for extraction from heat treated coals.5. Swelling experiments indicated a reduction in the degree of swelling due to heat-treatment. Exchanged calcium seems to suppress the swelling.6. Selectivity of cation exchange from mixed solutions of cobalt and nickel did not show any preference to a particular cation. Some dependence on pH of the solution was noted for the selectivity from cobalt-magnesium solution. The behavior can be explained on a basis of the radius of the hydrated cations.